The formation of S-S bonds is understood to be important in a number of oxidative biochemical processes. Conventional biochemical techniques have been used to investigate the oxidation of monothiols to disulfides in various proteins; however, such methods are limited in their accuracy and cannot be aplied in vivo. XAS is a non-destructive element-specific method for the study of bonding in a protein's native state. We propose to use S K-edge spectroscopy to probe sulfur bonding in amyloid proteins which form fibrils in several disease processes. We also plan to investigate the detoxification process by liver cells by determining the extent of disulfide formation, which is a measurement of oxidative stress. A second part of this sulfur XAS proposal involves experiments which are relevant to how the redox potentials of [Fe-S] clusters are related to electron transport processes in cell metabolism. S K-edge spectroscopy will be applied to investigations of the electronic environment around sulfur within the active site of iron-sulfur proteins. We also have a series of well characterized Mo-S compounds which serve as models for amide-sulfur H-bonding that is proposed to affect the electronic distribution in [Fe-S] active sites which we will study in conjunction with the biological samples. By determining the charge density on sulfur for a series of oxidized and reduced model compounds and various ferredoxins, a better understanding of electron transport and structure/functon relationships can be attained for these metalloproteins.